It is important for persons who formulate products to be able to predict rust and/or corrosion tendencies of hardware components in a particular media containing the product. This is best accomplished by providing those individuals with a fairly accurate assessment of corrosion rates and information pertaining to the behavior of components when contacted by a particular product. Essentially, any corrosion which occurs includes two types of reactions--electrochemical and chemical, i.e. oxidation. Typically, when this procedure is followed, it involves selecting a particular product and examining its anticorrosion performance in some appropriate machine or equipment and then putting it into actual use. However, if details of the interaction processes of the various products with metal surfaces with which they would normally come into contact during actual use were known, this would lessen the need to have any extensive and expensive experimental testing.
Corrosion essentially is a deterioration process which occurs when a metal reacts with the environment. A common place where corrosive degradation occurs in a petroleum system is a metal-oil-water interface. The electrochemical mechanism of the corrosion process occurs when a pure metal comes into contact with an aqueous corrosion media. The chemical or oxidation mechanism of the corrosion process occurs either at a pure metal-vapor interface or as a follow-up to an initial electrochemical mechanism of corrosion. Both mechanisms are generally well known in the art and are discussed in detail in several texts and publications. For example, reference is made to The Corrosion Handbook, by H. H. Uhlig, John Wiley & Sons, New York, (1963).
Normal corrosion tests performed in a laboratory involve several categories depending upon the end result of the studies desired. These include studying the corrosion mechanism; selecting the most suitable system for withstanding a particular environment; determining the environment in which a particular material or system can be satisfactorily employed; or providing controls for obtaining product uniformity. The present invention is directed towards providing a product formulator with information on the mechanism of the corrosion inhibition processes. The literature has frequently recommended using what is generally referred to as a polarization method of testing to examine the anodic and cathodic behavior of corroding metals in aqueous environments.
When iron corrodes in an aqueous solution, the occurrence of the electrochemical mechanism is most prevalent at the sites where anodic and cathodic reactions take place. The metal surface can be considered as a plurality of closely spaced anode and cathode cell sections with very minimal current passing between the cells, which imposes great difficulty in making direct measurements of the polarization to obtain the necessary data. These measurements are best accomplished by forcing the metal specimen either to be positively or negatively charged in comparison to the open circuit potential, i.e. the potential characterizing the behavior of metal in the actual in-use environment. This way the entire metal specimen is either made the anode or the cathode of the cell and the current flow between working electrode and auxiliary electrode can be examined. The results then are plotted graphically as a dependence between imposed potential and observed current. The experimental value of corrosion current is established from the graph in order to evaluate the corrosion rate.